Inflator having snap fit initiator

ABSTRACT

An inflator includes a housing formed by two cups. An initiator is snap fit into an opening of a cup before the cup is connected to the other of the two cups. Flexible fingers on the outer surface of the initiator are biased inwardly as the initiator is inserted into the opening and then snap radially outward into an annular groove disposed on the inside surface of the opening to hold the initiator in the opening. An O-ring is then placed around the initiator between a shoulder of the initiator and a wall of the cup to bias the initiator away from the cup to ensure that the initiator remains in position and to seal the inside of the cup from the atmosphere.

This a division of copending application Ser. No. 08/233,357, filed Apr.26,1994 pending.

BACKGROUND OF THE INVENTION

a. Field of Invention

This invention pertains to an improved inflator assembly, and moreparticularly to an improved inflator assembly for inflating an air bagused for protecting passengers in a motor vehicle during a crash.

B. Description of the Prior Art

Air bag systems have become accepted as the primary means of protectingmotor vehicle passengers from injury during crashes. It has beenestimated that within five years all passenger vehicles sold in theUnited States will be equipped with such systems. An important part ofthe air bag system is its inflator assembly, the component whichprovides the pressurized gas necessary to inflate the bag. Because itplays such a crucial role in the system, the inflator assembly must meetseveral important criteria. It must be sturdy and robust so that itoperates flawlessly years after its original installation without anyservicing. It must be strong so that it can withstand the internalpressures resulting from the rapid gas generation process. It must betamper proof so that it cannot be easily dismantled and tampered byunskilled personnel. It must be relatively small and light weight,especially if it is to be installed in the steering wheel for theprotection of the driver. It must be inexpensive to keep down theoverall price of the motor vehicles.

While there are several inflator assemblies presently available on themarket, none of them meet all of the criteria set forth above.

OBJECTIVES AND SUMMARY OF THE INVENTION

It is an objective of the present invention to provide an improvedinflator assembly which is sturdy and resistant to long-term wear andtear in an automobile so that it remains functional over long timeperiods without the need for servicing.

A further objective is to provide an inflator assembly which is madetamper-proof after assembly.

Yet a further objective is to provide an inflator assembly whichprovides a tortious path for gases generated within to insure theexpulsion of clean gas to the air bag.

Other objectives and advantages of the invention shall be describedbelow. Briefly, an inflator assembly constructed in accordance with thisinvention includes a housing formed by two cups positioned andinterengaged to define two chambers therein. After assembly the two cupsare interlocked to provide a tamper-proof enclosure. At least one of thecups is formed with several indentations arranged to permit the cup tobe grasped with a tool during assembly so that the cups can be rotatedrelative to each other.

Inside one of the chambers there is provided an initiator which sets offthe inflator assembly. Advantageously the initiator is snap fit withinthe housing to insure that it is initially positioned and remains at apredetermined location.

Also provided in the chamber is a canister of tablets made of a gasgenerating material. The canister is held in an interference fit withinthe housing to prevent it from moving either radially or axiallytherein. Also disposed in the housing is a ring-shaped retainer memberand a filter held in place by the retainer member. The retainer memberis inserted into the housing to support the filter so that the filterdoes not fall out during assembly. Within the housing there are passagesprovided for gases to flow from the initiator to the canister and fromthe canister through the filter and out of the assembly formed by theinterengagement of two cups into the air bag. These passages arearranged to insure that the gases change direction by at least 90° C.from the initiator to the filter. In this manner a turbulent flow iscreated to provide sufficient contact between the initiator gases andthe tablets for a fast inflator gas production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of an inflator assembly constructed inaccordance this invention;

FIG. 2 shows a bottom view of the assembly;

FIG. 3 shows a side-sectional view of the assembly taken along line 3--3in FIG. 2;

FIG. 4 shows a partial side-sectional view of the bottom cup; and

FIG. 5 shows an exploded view of the assembly.

DETAILED DESCRIPTION OF THE INVENTION

In the following directional terms such up, down, top, bottom and soforth are used in conjunction with the orientation of the drawings forthe sake of clarity. It should be understood that the assembly describedbelow may have a different orientation once it is installed in a motorvehicle.

Referring now to the Figures, an inflator assembly 10 constructed inaccordance with this invention consists of a housing 12 formed of twocups 14, 16. Upper cup 14 is formed of two concentric cylindrical walls,an outer wall 18, and an inner wall 20, both walls extending normallyfrom a base plate 22. Similarly bottom cup 16 is formed of twocylindrical walls 24, 26 extending normally from a base plate 28. Aperipheral flange 30 on cup 14 is used for mounting the assembly to anair bag module.

As described in Commonly assigned U.S. Pat. No. 5,201,542, the two cupsare secured together by a double threaded arrangement. Moreparticularly, the inner surfaces of walls 18, 20 are threaded and engagethe threads formed on the outer surfaces of walls 24, 26 respectively.In this manner, when the housing 10 is closed the two cups are engagedby the threaded co-axial annular couplings 32, 34.

Importantly, wall 24 of cup 16 is formed with an annular rib 36 disposedbelow the threads. In addition, wall 18 of cup 14 is formed with anaxially extending annular lip 38 extending below rib 36 when the twocups are threadedly engaged as described above and as illustrated byletter A in dotted lines in FIG. 3. After the two cups have beenengaged, this lip 38 is rolled over rib 36 to mechanically interlock thecups together, as shown in solid lines in FIG. 3 by letter B. Thismechanical interlock is provided to insure that after the two cups havebeen assembled, they cannot be opened and tampered with by unauthorizedpersonnel. In addition, the mechanical interlock provides somemechanical strength for the housing 12. Alternatively, or in addition tothe rib and lip arrangement described above, the two cups may also beinterlocked by providing holes in the cups and driving spikes 40 throughthe holes as shown in FIG. 3. Spikes 40 are preferably flush with theouter surface of wall 18 to insure that once they are driven in theycannot be removed.

As it can be best seen in FIG. 3, after the housing 10 is assembled, asubstantial portion of the bottom cup 16 is disposed inside, or at leastcovered by the top cup 12. Hence it is difficult to grasp the bottom cup16 properly to allow the two cups to be screwed together. In order tosolve this problem, bottom plate 28, which is substantially circular inshape, is provided peripherally with a plurality of scallops or notches42. The purpose of these notches is discussed below.

The two cups 14, 16 cooperate to form two chambers within housing 10, acentral chamber 44, and annular chamber 46 disposed coaxially aboutchamber 44. Chamber 44 is used to hold an initiator 48. Preferably,initiator 48 has a cylindrical body 50 having a diameter slightlysmaller than the diameter of hole 52 defined by wall 26 of cup 16. Nearthe top, initiator 48 has an annular enlarged portion 54 with adownwardly pointed shoulder 56. Below portion 54, initiator 48 isprovided with a plurality of flexing fingers 58 arranged annularly aboutbody 50. Each of these fingers 58 extends upwardly toward portion 54 andradially outwardly and are slightly flexible radially.

Hole 52 is formed with an inner annular groove 60 defined by a wallportion 62 extending upward and toward a radially inwardly orientedshoulder 64. The distance between shoulder 64 and the top surface 66 ofwall 26 is slightly smaller than the distance between the tips offingers 58 and shoulder 56 on portion 54.

The initiator includes wires 68, 70 used to send an electrical signal tothe initiator 48 for detonation. Wires 68, 70 are connected to anacceleration sensor disposed elsewhere in the system. Alternatively,initiator 48 may include a mechanical acceleration sensor in which casethe wires 68, 70 are omitted.

The wall 26 is thus arranged and constructed to engage with theinitiator 48 and hold the same in a preselected position inside thechamber 44. For this purpose, initiator 48 may be inserted into opening52 from the top downward. As the body 50 is moving inward into hole 52,fingers 58 are flexed radially inward. When the tip of the fingers 58reach groove 60 they snap radially outward thereby locking the initiator48 into the position shown in FIG. 3. In this position, wires 68, 70extend outwardly of hole 52 while the portion of initiator 48 disposedabove top surface 66 of wall 26 is disposed inside chamber 44. To insurethat the initiator 48 remains in this position and does not move or fallout, a resilient O-ring 72 is placed between top surface 66 and shoulder66. When the initiator is in place the O-ring 72 is squeezed in theaxial direction thereby providing an axial biasing force between theinitiator portion 54 and surface 66. In this manner O-ring 72 is pullingthe fingers 58 upward to remain in engagement with shoulder 64.Additionally, the O-ring 72 also forms a seal around body 50 to insurethat the chamber 44 is sealed off from ambient atmosphere.

Above initiator 48, chamber 44 is provided with a pellet 74 made of anauto-ignition material.

Chamber 44 communicates with chamber 46 through a plurality of holes 76.Preferably holes 76 are sloped downwardly at an angle of about 45° C.Chamber 46 is used to hold a canister 78 and a filter assembly discussedmore fully below. Canister 78 is generally annular in shape and has agenerally L-shaped cross section. The canister 78 is formed of twomembers, a wall member 80 which defines an annular cavity and aring-shaped cover member 82. The inner and outer edges of the covermember is rolled together with the inner and outer edges of the wallmember to form two annular seals 84, 86. These seals are also coveredwith a potting material as at 88, 90. In this manner the two members 80,82 form a hermetically sealed canister 78. Canister 78 is used to hold aplurality of tablets 92 which when heated above a preset temperaturerelease a gas very rapidly. A disk shaped member 94 is used to keep thetablets 92 above cover 82. Cover 82 is formed with a circular groove 96.This groove 96 is in contact with a circular ridge 98 formed on theinner surface of base plate 28.

Radially outwardly of canister 78, base plate 22 is provided with adownwardly extending annular wall 100 extending for a short distanceinside chamber 46.

Chamber 46 further holds a retaining ring 102. This ring 102 has twoannular portions, a substantially horizontal portion 104 and a verticalportion 106. Portion 104 is provided with a plurality of holes 107.Vertical portion 106 is sized so that it forms an interference fit withwall 100 as the ring 102 is inserted into cup 14.

As shown in FIG. 3, above the horizontal portion 104, there are providedtwo concentric annular filters, 108, 110. Filter 108 is a slag filterand it forms an annular space 112 with the vertical portion 106 of ring102.

Filter 110 is disposed radially outwardly of filter 108 and isconstructed and arranged to pick up fine particles from the gas flow.For example, filter 110 may be made of several layers of a finefiltration material made of paper, cloth, ceramic, and/or other filtermedia. Preferably the filter media is embedded at the two axial ends ina graphite seal 114, 116 used to insure that gases exiting the chamber46 do not by-pass the filter 110, however, other means of sealing can beused. As shown in the Figures, the outer wall 18 of upper cup 14 isprovided with a plurality of peripheral holes 118 for venting gassesthrough the filter 110.

The inflator assembly 10 is constructed as follows. The canister 78 isinstalled into the lower cup 16 and the initiator 48 is snapped intohole 52 from the top. The auto-ignition disk 74 is installed in theupper cup 14, inside wall 20. Filters 108 and 110 are pressed into theupper cup 14 in an inverted position and the retaining ring 102 ispressed on top of filters 108 and 110. Ring 102 may be positioned suchthat its holes 107 are angularly offset from holes 118 in cup 14.

The filters 108, 110 and ring 102 are maintained in this position by theinterference fit between ring wall 106 and wall 100. Therefore cup 14can be turned to the position shown in FIGS. 3 and 5 without the filters108, 110 and the ring 102 falling out therefrom.

Cups 14 and 16 are then placed into an abutting relationship and one orboth cups are turned so that they become threadedly engaged. During thisprocess the bottom cup 16 is grasped with a tool (not shown) havingengaging means for engaging the cup 16 by notches 42. Cup 14 and/or 16is turned until a torque in a preselected range is reached. For example,the cups can be turned until they are torqued at about 35 ft. - lbs.

Once the housing 10 is completed the inflator assembly is ready to beinstalled. As shown in FIG. 3, as the two cups 14, 16 are screwedtogether an upper edge 120 of lower cup 16 presses ring 102 upwardthereby squeezing the filters 108,110 and the graphite seals 114, 116between the horizontal ring portion 104 and base plate 22. At the sametime the portion of the canister 78 disposed under ring portion 104 isalso captured between ring 104 and base plate 28 of lower cup 16. Inthis manner the filters 108, 110 and canister 78 are effectively trappedbetween the base plates 22, 28 and ring 102 to prevent them frommovement. The registration between ridge 98 and groove 96 furtherinsures that the canister 78 does not shift in the radial or lateraldirection. Thus, the canister is prevented from rattling. This isimportant because if the canister rattles, the tablets contained thereinmay pulverize and thereby lose their effectiveness.

The inflator assembly operates as follows. The inflator assembly isnormally installed in the passenger compartment of a motor vehicle, forexample in the steering wheel. Initiator 48 is connected by wires 68, 70to a crash detector (not shown). When a crash is sensed by the detector,an electrical signal is received over wires 68, 70 which signal sets offthe initiator 48. The initiator 48 acts as a primer to generate arelatively small amount of gases. These gases quickly fill up chamber 44and flow through holes 76 toward chamber 46. The wall 80 of canister 78is constructed and arranged so that its wall section disposed in theimmediate vicinity of holes 76 is ruptured by the gases from theinitiator 48. The gases from the initiator then enter into the canisterand set off tablets 92. The tablets 92 then generate gases very rapidlyand at a relatively high pressure. These gases rupture the portion ofwall 80 disposed adjacent to holes 107 allowing gases to escape intospace 112. From this space, the gases exit through the filters 108, 110and holes 118. Importantly, holes 107 are positioned in such a mannerthat the gas flow through these holes is oriented at better than 90° C.with respect to the flow of gases through holes 76. In fact holes 107are oriented upwardly in an axial direction, i.e. in parallel withrespect to the axis X-X of inflator 10, while holes 76 are oriented at45° C. downwardly with respect to the axis, therefore the gas flowthrough these holes are oriented at a respective angle of 135° C. Thisfeature is important because it allows causes the gases to flowturbulently through the canister 78 and provide extended contact betweenthe initiator gases and the tablets 92 to insure that tablets 92 are setoff rapidly and uniformly. Otherwise the initiator gases could cause thecanister wall 80 to rupture prematurely allowing the initiator gases toescape through holes 107 before the tablets are fully set off.

The angular offset between holes 107 and 118 insure a turbulent flow ofgases from chamber 46 to the outside. In this manner as theses gasesflow through the filters 108, 110, they are cleaned better ofparticulate mater.

If the inflator assembly overheats, for example in case of fire, thepellet 74 ignites causing the tablets 92 to set off at a preselectedtemperature. Without the pellet 74, the assembly 10 could overheat to avery high temperature to set off tablets 92. By the time this hightemperature is reached, the housing 10 may be weakened and thereforewhen the tablets 92 are set off the gases generated which may causestructural distress.

Obviously numerous modifications may be made to the invention withoutdeparting from its scope as defined in the appended claims.

We claim:
 1. An inflator assembly for a passenger restraint systemcomprising:a housing including an inner cylindrical wall wall member,said inner cylindrical wall member being provided with a hole, saidhousing being so constructed and arranged to hold gas generatingmaterial; an initiator provided for setting off said gas generatingmaterial, said initiator including an outer initiator cylindrical wall,said initiator cylindrical wall and said inner cylindrical wall membercooperating to form an interference fit for supporting said initiator insaid hole, said outer initiator wall having a plurality of flexiblefingers disposed peripherally around and extending radially away fromsaid outer initiator wall, said fingers being deflected and biasedradially inwardly against the inner cylindrical wall member when saidinitiator is inserted into said hole; said inner cylindrical wall memberhaving an annular groove disposed peripherally around said hole withsaid fingers snapping into said groove after said initiator is insertedinto said hole; said flexible fingers and said annular groovecooperating to lock said initiator in a locked position in said hole toprevent said initiator from moving out of said hole; and said initiatorfurther including an annular shoulder axially spaced from said fingers,said assembly further comprising an O-ring disposed between saidshoulder and said inner cylindrical wall mounting for biasing saidinitiator.
 2. The assembly of claim 1 wherein said hole is formed toaccept said initiator from one direction, and wherein said groove isformed with a shoulder engaging said fingers.